The specific aims of this project are to: 1) define the regions and specific amino acid sequences of thrombospondin that participate in tumor cell and endothelial cell adhesion and migration on thrombospondin substrates, 2) identify cell surface receptors that mediate thrombospondin interactions with tumor and endothelial cells, 3) understand the mechanism for different cellular responses for thrombospondin binding to each class of receptor, 4) examine the relationship of thrombospondin gene expression in tumors and their metastatic phenotype.